A representative example of a scanning probe microscope (SPM) is an atomic force microscope. An atomic force microscope determines the shape of a specimen surface by measuring physical forces arising between the specimen and a cantilever probe, and has a configuration as shown schematically in FIG. 5.
FIG. 5 schematically illustrates the configuration of the major parts of the microscope, which comprises a cantilever 22 having a probe 27 at its tip, a laser light source 21, reflective mirrors 23 and 24, and quadrant photodetector 25. It will be noted that the size of the probe 27 and the cantilever 22 shown in FIG. 5 has been exaggerated in relation to the other elements.
Normally, laser light 26 from laser light source 21 is irradiated onto the top surface of the cantilever 22 via reflective mirror 23, and the resulting reflected light is inputted into the quadrant photodetector 25 via reflective mirror 24. In this state, as the probe 27 and specimen 29 are moved closer to each other to a distance of 1 nm or less, interatomic forces (attraction and repulsion) act between the atoms of the tip of the probe 27 and the atoms of the surface of the specimen 29 and the probe 27 moves up or down, and as a result, the cantilever 22 bends upward or downward. Due to the bending of the cantilever 22, the location where the reflected laser light enters the quadrant photodetector 25 changes. Due to the aforesaid change, the output of the quadrant photodetector 25 changes, and based on the change of this output, feedback control is performed by means of a scanner (not illustrated) in order to keep the distance between the probe 27 and the specimen 29 constant (i.e. to keep the interatomic forces constant). Therefore, by two-dimensionally scanning the probe 27 or specimen 29 while performing distance control between the probe 27 and the specimen 29, a concavoconvex image (constant force image) of the surface of the specimen 29 can be displayed on an image display device (not illustrated).
In an atomic force microscope, adjusting the position of the quadrupole photodetector and the laser light such that the laser light from the laser light source allows reflected light of highest intensity to be inputted into the center of the quadrupole photodetector is referred to as “optical axis adjustment.” Conventional optical axis adjustment has been carried out through manual operation by an operator.
The conventional optical axis adjustment procedure is presented below.
(First Operation)
While capturing the cantilever 22 and laser light 26 with an optical microscope 40 and checking the image filmed by video camera 41, a laser light adjustment knob (not illustrated) located in the atomic force microscope head (not illustrated) portion is turned to adjust the laser light irradiation location such that the laser light 26 is superposed over the cantilever 22 (referred to as coarse adjustment).
(Second Operation)
The laser light reflected from the cantilever 22 is projected onto a piece of paper directly in front of the quadrant photodetector 25, and the irradiation location of the laser light 26 is adjusted with a laser light adjustment knob (not illustrated) so that the laser light 26 is projected most clearly and roundly (referred to as fine adjustment).
(Third Operation)
The location of the quadrant photodetector 25 is adjusted so that the laser light 26 reflected from the cantilever 22 is irradiated onto the center of the quadrant photodetector 25.
It will be noted that Patent Literature 1 discloses a method in which optical axis adjustment is performed by imparting vibration for optical axis adjustment to the cantilever in a scanning probe microscope.
Furthermore, Patent Literature 2 discloses an optical axis adjustment method and optical axis adjustment aid using a laser light observation member having an irradiation surface wider than the area of the cantilever rear surface instead of the cantilever in a scanning probe microscope. Furthermore, Patent Literature 3 discloses a method of adjustment from outside the container of the quadrant photodetector in a scanning probe microscope installed inside a vacuum container.